176 FELSITIC LAVAS AND TUFFS NEAE CONWAY. [May 1 899, 



admirable paper on nodular felsites that the Author was so largely 

 indebted. The cutting at Bodlondeb was possibly not made when 

 the district was originally mapped by the officers of the Geological 

 Survey. With Gen. McMahon's observation, as to the resemblance 

 of sections of highly- altered tuffs with those of lavas which had taken 

 up rock-fragments, he fully agreed. In reply to Mr. Harker's query, 

 whether those rocks which were described in the paper as having 

 been originally obsidians were really devitrified glass, he explained 

 that such a conclusion was possible, although difficult of demon- 

 stration, since very slight alteration often sufficed to impart a 

 thoroughly lithoidal character, and such alteration might supervene 

 very soon after the solidification of an obsidian, Mr. Strahan's 

 remark that lava-flows accompanied by tuffs occurred south of the 

 general mass of felsite constituting Conway Mountain was very 

 interesting, as the occurrence had seemingly been overlooked 

 hitherto. 



In conclusion, he thanked the President and the Eellows for 

 their cordial reception of his paper. 



